Trash Gas

Title: Trash Gas
Author: Jim Mullarkey
Publication: The Outcrop, September 2004, p. 1, 6-8

Have you ever driven west on C-470? Just past the radio antennas west of Quebec Street, on the north side, maybe you’ve noticed some white pipes sticking out of the ground. As a reader of this periodical, interested in dirt, and pipes (?) it is possible you have seen one of the sites of Denver’s “trash gas” production, the County Line Landfill gas field. I was first introduced to the reality of natural gas production from landfills by Bob Raynolds in 1996 during an RMAG “On-the-Rocks” field trip. The bulk of this article is condensed from a presentation I put together in 2002. At the end is an abbreviated list of sources to access for additional and more current information on the topic of the conversion of landfill gas to more usable forms of energy.

Back to our journey along C-470, the County Line Landfill (CLLF) at South Colorado Boulevard and County Line Road collected and flared about 170 mcfd (312 cfpm) in early 2002. The CLLF is estimated to have made 1,171 MMCF of methane from December 1976 through December 2001. About 930 MMCF were used to generate electrical power, via a natural-gas-fired generator set, and about 241 MMCF have been flared. Given the current daily production this landfill will probably ultimately produce 1.3 BCF from 31 wells completed at depths of 40 ft to 100 ft in an approximately 100-acre field area. This field is also a true example of multiple use of land by a municipality, first as a landfill, then as a natural gas field, and now as a BMX track (see photos 1 and 2).

Lead story photo 1
Photo 1: Looking west from the BMX track at the CLLF. Foreground – wellhead; the fenced area encloses gathering system components including the vertical “John Zinc” flare stack at the north end of the enclosure. Colorado Boulevard is in the mid-ground.

BFI North America, a subsidiary of Allied Waste Industries, operates the Commerce City Tower Road Landfill (CCTRLF), adjacent to Denver International Airport (DIA), which was flaring about 304 mcfd (556 cfpm) of landfill gas, about 35% methane (CH4), in early 2002. This site is on the northeast corner of 88th Avenue and Tower Road. There are multiple wellbores visible on the outer slope of the landfill with a higher-elevation methane wellhead and an associated lower-elevation condensate wellhead (see photos 3 and 4). The operator has standard “oil industry” base maps showing approximately 100 wells and the gathering system. There was discussion at one time of using methane from landfills to produce energy to heat DIA.

The Environmental Protection Agency (EPA), in September 2001, listed 335 Landfill Gas Recovery and Utilization (aka Landfill Gas to Energy or LFGTE) projects as being active in the United States of America. The EPA also had at that time identified another 500 sites in the USA as presenting attractive opportunities for LFGTE project development. A perusal of the EPA website (address later in this story) in early 2004 indicates that now there are 340 active landfill gas energy projects and 600 other sites that offer attractive opportunities for development. There were no active LFGTE projects operating in Colorado as of late 2001. However, there are a number of Landfill Gas Recovery projects operating, and flaring methane, in Colorado, primarily as a control on methane emissions. Another metro Denver landfill gas recovery site is located at the Englewood Municipal golf course, on Oxford Avenue west of Santa Fe Drive. The golf cart storage area at this course cannot be enclosed due to potential methane gas buildups. In general, Colorado’s low annual precipitation and low humidity, coupled with its high altitude, make it less than ideal for economical conversion of landfill gas to energy.

Lead story photo 2
Photo 2: Close up of wellhead at the CLLF. Landfill methane flows out of the larger diameter pipe into the smaller diameter pipe.

The EPA is a government funnel point for landfill methane due to its focus on reduction of methane emissions as part of the program to reduce “greenhouse gas” emissions. The EPA uses a CH4 to CO2 equivalency for reduction assessment. In 2001, the EPA stated that landfill gas was the source of about 40% of the USA’s methane emissions. Much of the collection of landfill gas is a result of regulations and laws that were put in place in 1996 and 1998, which have required LFG collection systems in (mainly the larger) landfills for safety reasons. With the current focus on mitigating green-house gas emissions there is value (and profit?) in gathering and flaring or utilizing methane from landfills. Funding is available through the EPA; in 2002 grants ranging from $15,000 to $75,000 were available. The Renewable Energy Production Incentive gives a cash subsidy of up to 1.5 cents per kilowatt hour, which equates to several dollars per mcf of methane. Landfill gas production is not taxed and the gas volumes do not show up, for instance, in the Colorado Oil and Gas Commission records. Of course this is because the gas is a byproduct of organic matter concentrated by humans; the generating stratum was emplaced by the waste company, not natural events.

Lead story photo 3
Photo 3: Wellheads along the north side of the entrance road to CCTRLF.

Landfill gas or biogas, the gas generated from the decomposition of the organic matter in a landfill, is generally about 50% methane and 50% carbon dioxide.  The most efficient phase of gas generation occurs under anaerobic conditions. The peak methane generation phase is reached in between 9 months and 36 months after trash placement. The peak generation phase is long-lived; it can last up to 80 years. The ideal temperature for biogas generation is 41 degrees Celsius (105.8 degrees Fahrenheit,) and the ideal pH is between 6.8 and 7.2. Optimum conditions for methanogenesis occur at saturation levels (moisture levels) of greater than 40%; generation may be at a maximum at 99% saturation conditions. Some of this information is probably pertinent to some of the coalbed methane producers. A rule of thumb used by landfill gas operators is that 500 scfpm of biogas is convertible to 1 megawatt (MW) of electricity. This is given a 50% methane content of the biogas and sea level conditions for the engine efficiency. The engine burns the gas to drive a reciprocating engine to generate electricity from a generator set hooked to the engine and engines generate less horsepower (and therefore electricity) at higher elevations. Waste Management (www.wm.com) is touting a bioreactor landfill management technique where the landfill is designed to facilitate maximum biogas generation in a relatively short time. The landfill is designed to have wells in the landfill with the wells being used to re-inject the landfill leachate (and sometimes gases such as nitrogen and oxygen) to keep the landfill’s moisture content up and force anaerobic and or aerobic conditions on the landfill. Of course the wells are also designed and used to produce biogas.

Lead story photo 4
Photo 4: Looking south from 88th Avenue just east of Tower Road. Wellhead system – methane gathering wellhead up slope with a companion condensate sump on the lower portion of the slope.

A prospector looking for landfill gas-to-energy opportunities should certainly utilize precipitation and population maps. The EPA website has easy access to landfill information, including tons of waste in place (the population component), and date of initial operation, allowing estimation of organic maturity. Go to the EPA website listed at the end of this article, then go to the Database of Landfills and Energy Projects link on the left-hand margin, click on the state of Colorado on the United States map to view a list of operational projects, projects under construction, and candidate landfills. The list, a Microsoft Excel file, includes data on waste in place, methane generation rates, and other information such as annual waste acceptance rate (in tons per year). Some states, in addition, have a comprehensive landfill profile document. When available and filled out these forms contain a large amount of data helpful in assessing the landfill gas-to-energy potential of a particular site. With 4.7 million tons of waste in place, opened in 1972 and closed in 1991, it seemed to me that the Boulder, Colorado, landfill might be an attractive opportunity in Colorado. But most of the newer startup landfill gas-to-energy projects appear to be in wetter regions, with annual precipitation of over 25 inches.

Two Landfill Gas-to-Energy projects in Ohio (with about 35″ of annual precipitation compared to Denver’s 15″ or so), that were commissioned in the early 2000’s may be possible models for economic Landfill Gas-to-Energy projects. Carbon Limestone Landfill was flowing about 1.7 mmcfd of methane in the second quarter of 2002 with the EPA landfill profile sheet quoting a 14.9-MW electrical generation capacity rating and the Lorain County Landfill was flowing 0.8 mmcfd of methane and with an 8.1-MW electrical generation capacity rating quoted. These two projects utilize module 1.3-MW electrical generation units and have wells drilled on one-acre patterns. The wells are completed at depths of 100′ to 150′ and produced through pre-perforated 12 inch diameter PVC pipe with a gravel pack in the 36-inch borehole. They say they definitely have some good wells and some poor wells, similar to the oil industry.  They have done some CO2 wellbore cleanouts to push trash and silt away from the wellbore. Water production is their biggest problem; in some of the older fields they drop pumps into the wells to pump off the water. The end users are municipal power companies.

There are a large number of operational international landfill gas-to-energy projects ongoing, including over 20 projects in Australia and several in the United Kingdom. In Australia they are also working on a SWERF process, involving four principal steps: 1) a waste treatment and separation process, creating an organic pulp used for input to a (step 2) pyrolysis (gasification) process of carbon-based materials to create a syngas for power generation, (step 3) gasification of the residual carbon from step 2, and (step 4) generation of electricity from combustion of the syngas.

Landfill gas to energy appears to be a growing technology, with some surprising offshoots. The Rocky Mountain News had an article in its March 24, 2002, issue on the conversion of pig manure to biogas.  Most everyone would agree that converting landfill gas to energy is a good idea, but it appears to be marginally economic for the private sector. The LFGTE technology has the potential to be useful in two ways: 1) decrease methane emissions, and 2) create usable energy while decreasing emissions. Landfills also have the potential to provide assistance to the coalbed methane portion of the petroleum industry by acting as natural laboratories for the study of bacterial generation of methane. The methane recovery from coals at Drunkard’s Wash Field in Utah is reported to be enhanced with the “additional” methane generated by bacteria. Coalbed methane producers might consider creating a wellbore and reservoir environment friendly to methane-generating bacteria by varying moisture and temperature conditions, and they might evaluate and possibly apply bioreactor concepts. The LFGTE industry typically uses “blowers” or fans instead of compressors in their gathering systems; this also might have application in the natural gas industry.


General references

Hutchinson, Peter M.,1993, An energy perspective on landfill gas, in “The Future of Energy Gases,” U.S. Geological Survey Professional Paper 1570, p.365-382.

Rice, Dudley D., 1993, Biogenic Gas: Controls, Habitats, and Resource Potential, in “The Future of Energy Gases,” see preceding citation, p. 573 – 606.

The website of the U.S. Environmental Protection Agency’s Landfill Methane Outreach Program: http://www.epa.gov/lmop/. You can use the RMAG website http://www.rmag.org as a steppingstone to the EPA site.

The website of the Solid Waste Association of North America at http://www.swana.com contains some excellent information on landfill gas (go to the site and then to the Educate link on the left hand margin, then to technical divisions, then to landfill gas). This site is also a great source of information on the government involvement in landfill gas.

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